Four people were shot and killed and several others were hospitalized during one of the more violent 30 hours in San Diego in recent memory.

The slayings bring to 21 the number of homicides in San Diego so far this year, a 50 percent increase over the same period last year. Further, the 65 homicides for all of 2003 marked a nearly 40 percent increase from the 47 the year before.

"There isn't one thing that we can put our finger on as to why this all happened," said Capt. Jim McGinley, who commands the homicide, robbery, special investigations and financial crimes units.

The dead ranged in age from 17 to 52. Police believe one of the slayings was gang-related.

The most recent shooting occurred about 6 a.m. yesterday when a 24-year-old man was shot and fatally wounded on 63rd Street in Encanto. He died at a hospital about 90 minutes later.

No one has been arrested.

A witness told police that the victim had been driving a small white pickup in the area.

"The resident noticed the victim driving the truck eastbound on Madrone Avenue, then turning around and driving westbound before pulling into the west curb of 63rd Street, near Imperial Avenue," said San Diego police homicide Lt. Kevin Rooney.

When the man stepped out of the truck, he was approached by several young males, Rooney said. Some residents then heard popping noises and looked out of their homes to see the man lying on the sidewalk.

Police believe the shooting may have stemmed from an argument.

One resident said he believed the victim is the same person who knocked on his door shortly before 6 a.m.

"It was too early to answer the door, so I didn't," he said. "I don't know what he wanted."

The victim's name is being withheld until his family can be notified.

Twelve hours earlier, a 24-year-old man was shot dead in front an apartment complex on Altadena Avenue in Talmadge, police said. The man and a companion were standing outside when a third man approached from the west alley, exchanged words and opened fire. The shooter got into a vehicle that headed south, before going west on El Cajon Boulevard.

Police believe the shooting may have been sparked by a disagreement over a girl and may be gang-related. No one has been arrested.

The victim was identified as Angel Manuel Mendoza of 65th Street.

About 5 p.m. Sunday, Margaret Schmidt, 52, was shot dead in her Encanto home when a weapon apparently accidentally discharged as her 24-year-old son was demonstrating a new laser light attachment to his gun, police said.

No one has been arrested.

About 1 a.m Sunday, a teen was shot dead at a Jack in the Box on South 43rd Street in Southcrest.

Ramon Gomez Jr., 17, of Lincoln Park was killed, and a 19-year-old man was shot in the back in an attack apparently motivated by a dispute between two groups, police said.

Other violent attacks included a man being stabbed in the head on Market Street in East Village about 1 a.m. Sunday; shots being fired into a house on Streamview Drive in Oak Park about 12:45 a.m. Sunday; and a 20-year-old man being shot twice in the head with a small-caliber handgun in a parking lot of a Denny's Restaurant on Camino Del Rio South about 2:30 a.m. Sunday.